1. Field of the Disclosure
The present disclosure relates to a semiconductor device and method for manufacturing the same, in particular, to a semiconductor device using aluminum alloy as its metal gate and a method for manufacturing the same.
2. Description of the Related Art
As dimensions of semiconductor devices are continuously shrinking, the size of the gate structure and the thickness of the gate insulating layer are correspondingly decreased. However, the leakage current may become excessively large when the gate silicon oxide insulating layer is too thin. To reduce the leakage current, a high-dielectric-constant (high-k) material, rather than silicon oxide, is used for the gate insulating layer. However, a polysilicon gate may react with the high-k material, resulting in issues like a gate depletion effect and a boron penetration problem, which can degrade the device performance. Therefore, metal materials are used for gates to replace polysilicon.
High-k metal gates have become a mainstream solution. Usually, the metal gates are formed of aluminum. In the processes of making an aluminum gate, chemical mechanical polishing (CMP) for planarizing the aluminum gate is very critical. However, as aluminum is an active metal, during the CMP and subsequent cleaning processes, it is prone to corrosion in acid or alkali environments. If aluminum corrosion such as pits occurs on aluminum gates, device performance and reliability can be greatly degraded.